It was common place at one time, did it on SGB for years as stated in an earlier post it suits barrow access.
This was covered in BS5973 10.2
"Ledger bracing from the inside ledger to the guardrail level of the lift below may be used provided that every pair of standards is so braced instead of every alternate pair".
It was also covered in TG20 6.2, paragraph 4
"Ledger bracing from the inside ledger to the principle Guardrail level of the lift below may be used on unclad fully boarded scaffolds provided that every pair of standards is so braced instead of every alternate pair".
NOTE the inclusion of UNCLAD